Conventional footwear products, and particularly athletic shoes, have included two primary elements, namely an upper member and a sole member or structure. The upper member provides a covering for the foot that securely receives and positions the foot with respect to the sole structure. In addition, the upper member may have a configuration that protects the foot and provides ventilation, thereby cooling the foot and removing perspiration. The sole structure generally is secured to a lower portion of the upper member and generally is positioned between the foot and the ground. In addition to attenuating ground reaction forces, the sole structure may provide traction and control foot motions, such as pronation. Typically, the sole structure is attached to the upper member, e.g., using adhesives, stitching, welding, etc. Accordingly, the upper member and the sole structure operate cooperatively to provide a comfortable structure that is suited for a variety of ambulatory activities, such as walking and running.
The sole member or structure of athletic footwear generally has exhibited a layered configuration that includes a comfort-enhancing insole, a resilient midsole formed from a polymer foam material, and a ground-contacting outsole that provides both abrasion-resistance and traction. The midsole is the primary sole structure element that attenuates ground reaction forces and controls foot motions. Suitable polymer foam materials for the midsole include ethylvinylacetate or polyurethane that compress resiliently under an applied load to attenuate ground reaction forces. Conventional polymer foam materials are resiliently compressible, in part, due to the inclusion of a plurality of open or closed cells that define an inner volume substantially displaced by gas. Additional elements that attenuate ground reaction forces, or impacts, may include fluid-filled bladders that compress and deform to absorb the impact and thereby cushion the foot during the impact.
The present invention generally relates to new and novel sole structures for footwear that include one or more fluid-filled bladders.